The issue checker scans your entire app to detect problems. On larger apps this process can take a significant amount of time, and in some cases the checker is still running when you deploy — meaning a newly introduced issue might not be flagged before the deployment goes through.
What you might notice
The issue checker takes a long time to complete on first load or after changes
You deploy your app and discover an issue that the checker hadn't flagged yet
Workaround
Wait for the issue checker to fully complete before deploying, especially after making significant changes. You can monitor the indicator in the editor toolbar to confirm when the check has finished. You can read more about the issue checker in the documentation.